A CRT is evacuated to a very low pressure and accordingly is subject to the possibility of implosion due to the stresses produced by atmospheric pressure acting on all surfaces of the CRT. This problem has been addressed in the art by providing the CRT with an implosion protection band. Such a band is used to apply a compressive force to the sidewall of a faceplate panel of the CRT to redistribute some of the forces. The redistribution of the forces decreases the probability of an implosion of the tube by minimizing tension in the corners of the panel. An implosion protection band is also beneficial because it improves the impact resistance of the tube. Glass in compression is stronger than glass which is in tension and the band causes compression in the panel areas which otherwise would be in tension. The implosion protection band also provides a convenient structure on which to attach a degaussing coil that is used to remagnetize internal ferromagnetic components of the CRT.
It is known that the earth's magnetic field affects the paths of the three electron beams emitted by a CRT electron gun and may cause what is called "misregister" in a color CRT. A shadow mask having a multiplicity of apertures therethrough is located in proximity to a tricolor color screen of the tube to assure that each of the three electron beams impacts the phosphor element of the proper light emitting color. Thus, for example, the electron beam which is modulated the red information impacts the phosphor element which emits red light. Because the electrons of the beams are charged particles, the earth's magnetic field has an influence on their trajectories which can cause the electrons to impact a phosphor of the improper color, causing misregister, thereby degrading the quality of the image display. For this reason, a magnetic shield, preferably an internal magnetic shield, or IMS, is used within the CRT to act in conjunction with the shadow mask and its frame to shield a substantial portion of the electron beams trajectories from the influence of the earth's magnetic field. The shielding acts in the following way: the external magnetic field realigns the Weiss domains in the ferromagnetic material, creating an induced magnetic field that tends to oppose the action of the external field of the earth which has given rise to it. If the material of the ferromagnetic components, i.e., of the shadow mask, mask frame and the IMS, has high magnetic permeability, the induced field at least partially opposes the external field. Hence, the deleterious effect of the earth's magnetic field is reduced.
For more efficient compensation, the ferromagnetic material of the components has to be de-magnetized with a magnetic field that is provided by the degaussing coil, fixed by appropriate means to the rear of the tube and overlying the ferromagnetic components. Such arrangement is described in, for example, U.S. Pat. No. 5,347,367, in the names of Swank et al., entitled, Cathode-Ray Tube Having Implosion Protection Means With Openings. In the Swank et al., Patent, a plurality of openings are formed in the implosion protection means to support a degaussing coil. It may be desirable to attach the degaussing coil without using such openings. Advantageously, by eliminating the openings, the implosion band may be narrower than when such openings are used.